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Topic: Powering a small hobby servo and a small motor (Read 4541 times) previous topic - next topic

nickl87

Hi everyone

I am creating a bubble machine which uses a small hobby servo for dipping some metal wire into a bowl of soap water and a small motor for turning a fan.

My problem is that the arduino cannot run these on its own power supply, when powered by usb.

My question is can it run these if I purchase a 9v adapter? Or is the only solution to power one of them from a battery pack?

I know this is a pretty easy question if you know something about electronics, and I am computer science educated, however mostly with focus on software not hardware.

PaulS

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can it run these if I purchase a 9v adapter?

An electron pushed by a battery or by an power plant miles away is still an electron. Moving electrons produce current. Current makes motors move.

As long as the 9V wall wart can produce sufficient current to power the servo and the fan at the same time, you can use it.

Sounds like a cool project.

retrolefty

#2
Jan 23, 2011, 08:54 pm Last Edit: Jan 23, 2011, 08:55 pm by retrolefty Reason: 1
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My question is can it run these if I purchase a 9v adapter? Or is the only solution to power one of them from a battery pack?


Plugging a 9vdc wall wart adapter into the external power connector of your Arduino may not solve your problem at all. The USB power is limited to 500ma by a fuse. Any external power used via the external power connector goes to a on-board +5vdc regulator. So if you still try and wire your servo and motor from the Arduino +5vdc the current will be limited to the on-board 5vdc regulators current limit, which may be a little higher the USB 500ma, but not a lot more.

Any time you need to power external devices that require larger amounts of current in excess of the Arduinos +5vdc current limit, is best done with suitable external power supplies wired directly to the devices. You need to be sure what voltages those devices require and if they need regulated voltage or not, and of course how much current the devices require.

There is no simple answer, only specific needs for specific devices. One needs to know the voltage and maximum current requirements for all external devices before the best power management solution can be determined.

Lefty


Stijntjhe

#3
Jan 23, 2011, 10:57 pm Last Edit: Jan 23, 2011, 10:57 pm by Stijntjhe Reason: 1
Servos are made to work on 5volt, correct me if i'm wrong.
And about the other motor for the fan, use a relay?

retrolefty

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Servos are made to work on 5volt, correct me if i'm wrong.


Correct, typically 4.5 to 6vdc. That however doesn't tell us how much current they require as start-up and at full mechanical load. An Arduino can supply +5vdc for external use, but it has a limit of how much current it can provide. That is the issue the OP is looking at.

I usually recommend budgeting one amp of 5vdc current for each servo attached. Might be a little liberal, but then what would you recommend?

Lefty

cr0sh

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I usually recommend budgeting one amp of 5vdc current for each servo attached. Might be a little liberal, but then what would you recommend?


That's probably a good rule of thumb for general hobby servos. Especially if you don't have any specs. However, some servos come with (or can be obtained) datasheets that list this information, so if you have that, use it.

This is especially important if you are trying to control 1/4 scale servos, or sail-winch servos which are much larger; those likely pull way more than an amp of current.

Finally - servos and DC motors don't generally require voltage regulation, you just need to know their current requirements so you can properly size the power supply.

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Ran Talbott

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a small motor for turning a fan

Does this motor have a name?   :)

It's hard to give advice on which power supply to choose when you don't know what's being powered.

It's possible that you can get away with one power supply, but you might need 2, or even 3.

In the immortal words of the Magic 8 Ball: Reply hazy, try again later  ;)

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